Expandable interbody fusion implant

ABSTRACT

Disclosed is an expandable interbody fusion implant that is configured to have an initial configuration having a first footprint width suitable for being inserted into an intervertebral space and an expanded configuration having a second footprint width that is greater than the first footprint width. The implant may include a first body member and a second body member that is pivotally coupled to the first body member. The implant may be expanded using an inflatable balloon. The implant may be expanded bilaterally such that both body members rotate relative to the other or the implant may be expanded unilaterally such that one of the body members rotates relative to the other.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.16/108,211, filed Aug. 22, 2018, which is a continuation of U.S. patentapplication Ser. No. 15/334,816, filed Oct. 26, 2016, which is acontinuation of U.S. patent application Ser. No. 13/920,652, filed Jun.18, 2013, which is a continuation of U.S. patent application Ser. No.13/033,119, filed Feb. 23, 2011, the contents of all of which are herebyincorporated by reference as if set forth in their entireties herein.

BACKGROUND

Historically, complete removal of a disc from between adjacent vertebraeresulted in fusing the adjacent vertebrae together. This “interbodyfusion” procedure, which is in use today, is a widely accepted surgicaltreatment for symptomatic lumbar and cervical degenerative disc disease(DDD). The aim of a spinal fusion is to relieve pain caused by adegenerated disc, restore anatomy (disc height and/or lordoticcurvature), and immobilize the affected level (fusion). Such implantshave mainly been inserted into lumbar and cervical intervertebral spacesbetween adjacent vertebral bodies through an anterior, antero-lateral(oblique), lateral, extraforaminal, transforaminal, or posteriorsurgical approach.

In most cases of interbody fusion, the main objective is to relieve painwhile preventing iatrogenic injury. Moreover the interbody device shouldbe stable and subsidence resistant. In order to prevent iatrogenicinjury during interbody fusion, a minimally invasive approach offers anideal solution, however, in order to provide stability and subsidenceresistance, a large footprint is beneficial. Therefore, a compromise isgenerally required to achieve both.

While many minimally invasive interbody fusion devices are offered in afixed shape, some are available that include an expandable footprint.These expandable devices, however, are not ideal and improvements aredesired.

SUMMARY

Disclosed is an expandable interbody fusion implant that is configuredto have an initial unexpanded configuration having a first footprintwidth suitable for being inserted into an intervertebral space definedby a pair of adjacent vertebral bodies, and an expanded configurationhaving a second footprint width that is greater than the first footprintwidth. The implant may be expanded from the initial configuration to theexpanded configuration either bilaterally or unilaterally.

In one embodiment the implant may include a first body member and asecond body member that is pivotally coupled to the first body memberabout a pivot axis. The first body member may have a first cage body andthe second body member hay have a second cage body. The implant may alsoinclude a channel that extends at least partially through at least oneof the first and second cage bodies, the channel configured to receivean inflatable balloon. The second body member may be configured to beadjacent the first body member, such that expansion of the inflatableballoon biases the first and second body members away from each other,thereby causing the implant to move from the initial configuration tothe expanded configuration.

In another embodiment the implant may include a first body member and asecond body member that is pivotally coupled to the first body member.The first body member may be configured to be braced against a vertebralsurface. The first body member may include a first elongate cage body.The first elongate cage body may define superior and inferior boneengaging surfaces. The first elongate cage body may have a free end. Thesecond body member may include a second elongate cage body. The secondelongate cage body may define superior and inferior bone engagingsurfaces. The second elongate cage body may have a free end. The implantmay be configured to receive an expandable element, such that when theexpandable element is expanded at least the second body member pivotswith respect to the first body member so as to move at least the freeend of the second body member relative to the free end of the first bodymember and expand the implant to the expanded configuration.

Also disclosed is a method of implanting an intervertebral implant intoan intervertebral space that is defined by a superior vertebral body andan inferior vertebral body that are opposed in a transverse direction.According to the method, an expandable implant may be inserted into theintervertebral space. The implant may have a first width duringinsertion. The implant may include a first body member, and a secondbody member pivotally coupled to the first body member. The first andsecond body members may each include a fixation element receivingaperture. An inflatable balloon may then be positioned within theimplant. By inflating the balloon, the implant may expand in a directionthat is substantially perpendicular to the transverse direction. Theimplant may expand to a second width that is greater than the firstwidth.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing summary, as well as the following detailed description ofillustrative embodiments of the interbody fusion implant of the presentapplication, will be better understood when read in conjunction with theappended drawings. For the purposes of illustrating the interbody fusionimplant of the present application, there is shown in the drawingsillustrative embodiments. It should be understood, however, that theapplication is not limited to the precise arrangements andinstrumentalities shown. In the drawings:

FIG. 1A is a side perspective view of a pair of vertebral bodiesseparated by an intervertebral space;

FIG. 1B is a side perspective view of an expandable intervertebralimplant in accordance with one embodiment, the implant inserted into theintervertebral space shown in FIG. 1A, the implant expandable between anunexpanded configuration having a first footprint width, and an expandedconfiguration having a second footprint width that is greater than thefirst footprint width;

FIG. 2A is a side perspective view of the expandable intervertebralimplant shown in FIG. 1B, the implant including a first body member anda second body member pivotally coupled to the first body member, eachbody member having a plate and a cage body;

FIG. 2B is a an exploded view of the implant shown in FIG. 2A;

FIG. 2C is a cross-sectional side perspective view of the implant shownin FIG. 2A;

FIG. 2D is a cross-sectional side perspective view of the implant shownin FIG. 2C, the implant receiving an expandable element in a channeldefined by the first body member;

FIG. 2E is a cross-sectional side perspective view of the implant shownin FIG. 2D, with the expandable element in an expanded configuration tothereby expand the implant to its expanded configuration;

FIG. 3A is a side perspective view of the implant shown in FIG. 2Apositioned in the intervertebral space while in the unexpandedconfiguration, the superior vertebral body is removed for clarity;

FIG. 3B is a side perspective view of a first fixation element beinginserted into a first fixation element receiving aperture of the firstbody member of the implant shown in FIG. 3A;

FIG. 3C is a side perspective view of the first fixation element fullyinserted into the first fixation element receiving aperture of theimplant so as to affix the first body member of the implant to thesuperior vertebral body;

FIG. 3D is a top plan view of the implant shown in FIG. 3C;

FIG. 3E is a side perspective view of the implant shown in FIG. 3D,after the implant has been expanded to its expanded configuration;

FIG. 3F is a top plan view of the implant shown in FIG. 3E;

FIG. 3G is a side perspective view of a second fixation element beinginserted into a second fixation element receiving aperture of the secondbody member of the implant shown in FIG. 3F;

FIG. 3H is a side perspective view of the second fixation element fullyinserted into the second fixation element receiving aperture of theimplant so as to affix the second body member of the implant to theinferior vertebral body;

FIG. 3I is a side elevation view showing the implant of FIG. 3H affixedto the superior and inferior vertebrae;

FIG. 4A is a cross-sectional side perspective view of an expandableintervertebral implant in accordance with another embodiment, theimplant including a first body member and a second body member that arespaced apart so as to define a cavity therebetween, the cavity receivingan expandable element; and

FIG. 4B is a cross-sectional side perspective view of the implant shownin FIG. 4A, with the expandable element in an expanded configuration tothereby expand the implant to its expanded configuration.

DETAILED DESCRIPTION

Referring to FIGS. 1A and 1B, a superior vertebral body 10 a defines asuperior vertebral surface 14 a of an intervertebral space 18, and anadjacent inferior vertebral body 10 b defines an inferior vertebralsurface 14 b of the intervertebral space 18. Thus, the intervertebralspace 18 is disposed between the vertebral bodies 10 a-b. The vertebralbodies 10 a-b can be anatomically adjacent vertebral bodies, orremaining vertebral bodies after a vertebral body has been removed froma location between the vertebral bodies 10 a-b. As illustrated, theintervertebral space 18 is illustrated after a discectomy, whereby thedisc material has been removed or at least partially removed to preparethe intervertebral space 18 to receive an intervertebral implant 26, asshown in FIG. 1B, that can achieve height restoration. Theintervertebral space 18 can be disposed anywhere along the spine asdesired, including at the lumbar, thoracic, and cervical regions of thespine.

Certain terminology is used in the following description for convenienceonly and is not limiting. The words “right”, “left”, “lower” and “upper”designate directions in the drawings to which reference is made. Thewords “inner” or “distal” and “outer” or “proximal” refer to directionstoward and away from, respectively, the geometric center of the implantand related parts thereof. The words, “anterior”, “posterior”,“superior,” “inferior,” “medial,” “lateral,” and related words and/orphrases are used to designate various positions and orientations in thehuman body to which reference is made and are not meant to be limiting.The terminology includes the above-listed words, derivatives thereof andwords of similar import.

The implant 26 is described herein as extending horizontally along alongitudinal direction “L” and lateral direction “A”, and verticallyalong a transverse direction “T”. Unless otherwise specified herein, theterms “lateral,” “longitudinal,” and “transverse” are used to describethe orthogonal directional components of various components. It shouldbe appreciated that while the longitudinal and lateral directions areillustrated as extending along a horizontal plane, and that thetransverse direction is illustrated as extending along a vertical plane,the planes that encompass the various directions may differ during use.For instance, when the implant 26 is implanted into an intervertebralspace, such as the intervertebral space 18, the transverse direction Textends vertically generally along the superior-inferior (orcaudal-cranial) direction, while the horizontal plane defined by thelongitudinal direction L and lateral direction A lies generally in theanatomical plane defined by the anterior-posterior direction, and themedial-lateral direction. Accordingly, the directional terms “vertical”and “horizontal” are used to describe the implant 26 and its componentsas illustrated merely for the purposes of clarity and illustration.

Referring now to FIGS. 1B and 2A-2E, the interbody expandable implant 26is configured to be positioned within an at least partially cleared outdisc space, such as the disc space 18 disposed between the superiorvertebral body 10 a and the inferior vertebral body 10 b. The implant iselongate in the longitudinal direction L and defines a distal end D anda proximal end P. The implant 26 is expandable between a first initialunexpanded configuration having a first footprint width, and a secondexpanded configuration having a second width that is greater than thefirst width. The implant 26 may be implanted while in the unexpandedconfiguration so as to provide a minimally invasive approach for theprocedure. Once positioned within the intervertebral space, the implant26 may be expanded in situ to its expanded configuration so as toprovide an adequate footprint for an interbody fusion device. Theexpanded implant 26 may achieve improved stability and may reducesubsidence risk. The implant 26 can be formed entirely from or partiallyfrom a range of biocompatible materials or combinations of materials,including polymers, such as PEEK, porous PEEK, carbon fiber-reinforcedPEEK, titanium and titanium alloys, stainless steel, ceramic, polylacticacid, tantalum, and magnesium, or even allograft bone.

As shown in FIGS. 2A-2E, the implant 26 includes a first body member 30and a second body member 34 that is pivotally coupled to the first bodymember 30 at a hinge 38. At least one of the first body member 30 andthe second body member 34 may rotate about the hinge 38 relative to theother to thereby expand the implant 26 to its expanded configuration. Asshown, the first and second body members 30 and 34 may rotate in thehorizontal plane. That is, after the implant 26 has been implanted intoan intervertebral space that is defined between adjacent vertebralbodies that are opposed in the transverse direction T, the first andsecond body members 30 and 34 may rotate in a plane that issubstantially perpendicular to the transverse direction T, so atincrease the overall footprint of the implant 26. The implant 26 isconfigured such that both body members 30 and 34 may rotate so as toprovide bilateral expansion of the implant. The implant 26 may also beconfigured such that only one of the body members 30 and 34 rotatesrelative to the other so as to provide unilateral expansion. Suchunilateral expansion may be desired if the implant is positionedanterior using a lateral approach. Because in such a case the majorvessels (aorta and vena cava) reside anterior to the vertebral column, abilateral expansion may damage the vessels. Therefore, one of the bodymembers 30 and 34 may be affixed to a vertebra prior to expansion of theimplant 26 to thereby allow for unilateral expansion of the implant andprevent any damage to the vessels.

As best shown in FIGS. 2B and 2C, the first body member 30 includes afirst plate 40, and a first cage body 44 that is coupled to the firstplate 40. In particular, the first plate 40 is coupled to a proximal endof the first cage body 44. While the first plate 40 and the first cagebody 44 are shown as separate components that are coupled together, itshould be understood that the first plate 40 and the first cage body 44may be integrally formed as one piece.

As best shown in FIG. 2B, the first plate 40 includes a front facemember 42 that defines a fixation element receiving aperture 48 thatextends therethrough from a front side to a back side at an upwardangle. The fixation element receiving aperture 48 may define internalthreads that are configured to engage external threads defined by afixation element, such as bone screw 52, as the bone screw 52 isinserted into the fixation element receiving aperture 48. The bone screw52 is configured to engage the superior vertebral body 10 a once it isfully inserted to thereby brace or otherwise affix the first body member30 to the vertebral body. The fixation element receiving aperture 48 maybe fully enclosed as shown in the illustrated embodiment, or thefixation element receiving aperture 48 may be partially enclosed tothereby define for example a semi-circle. The fixation element receivingaperture 48 may be configured to receive a fixation element other thanthe bone screw 52. For example the fixation element receiving aperture48 may be configured to receive blades or nails. Therefore, the fixationelement receiving aperture 48 may be void of threads. Moreover, itshould be understood that the first body member may be configured to bebraced against the vertebral wall of the vertebral body using structureother than fixation elements. For example, the first body member 30 maybe toothed so as to not allow the first body member 30 to rotate whenthe implant is inserted.

As shown in FIG. 2B, the first plate 40 also defines a curved internalsurface 56 that is generally concave. As shown, the curved internalsurface 56 is positioned such that it is adjacent the second body member34. As will be discussed, the curved internal surface 56 allows thefirst body member 30 to rotate relative to the second body member 34without substantial interference from the second body member 34.

As shown in FIGS. 2A and 2B, the first cage body 44 is elongate in thelongitudinal direction L. The first cage body 44 defines an upper orsuperior or outer transverse bone engagement or contacting surface 60configured to contact the superior vertebral body 10 a, and a lower orinferior or outer transverse bone engagement or contacting surface 64configured to contact the inferior vertebral body 10 b. Both outercontacting surfaces 60 and 64 may include teeth 68 that are configuredto engage the superior and inferior vertebral bodies 10 a and 10 b. Asshown, the teeth 68 may be aligned in arcs with the centre of these arcsbeing proximate to the hinge 38.

As shown in FIG. 2B, the first cage body 44 includes an elongate bodyportion 70 that extends in the longitudinal direction L, and a firstjoint 74 that extends proximally from the elongate portion 70 and atleast partially toward the second body member 34. In the embodimentshown, the joint 74 extends substantially perpendicularly from theelongate portion 70 toward the second body member 34. As shown, the cagebody 44 also includes a free end 78 that extends distally from theelongate body portion 70 and at least partially toward the second bodymember 34. Therefore, because both the first joint 74 and the free end78 at least partially extend toward the second body member 34, the firstcage body 44 generally defines a C-shaped structure.

As shown, the first joint 74 includes a pair of plates 82 that arespaced apart so as to define a gap 86 between the two plates 78. Eachplate 82 defines an aperture 90 that extends completely therethrough inthe transverse direction T. As shown, each aperture 90 is aligned and isconfigured to receive a pin 94 as shown in FIG. 2C.

The free end 74 of the first cage body 44 defines a first mating feature94. As shown, the first mating feature 94 includes a recess 98 thatextends into the curved portion of the free end 74. The recess 98 isconfigured to receive a mating feature that is defined by the secondbody member 34 when the implant 26 is in an unexpanded configuration.

As best shown in FIG. 2C, the first body member 30 also defines achannel 102 that extends longitudinally through the first body member30. That is, the channel 102 extends at least partially through thefirst joint 74, through the elongate body portion 70, and into therecess 94 defined by the free end 78. A shown, the channel 102 defines anon-linear path 106 from a proximal end of the implant 26 to the distalend of the implant 26. As shown in FIGS. 2D and 2E, the channel 102 isconfigured to receive an expandable element 110 so as to guide theexpandable element 110 along the path 106 toward the recess 98. Theexpandable element 110 is configured to expand the implant 26 to itsexpanded configuration when the expandable element 110 has beenactivated. In the embodiment shown, the expandable element 110 is aninflatable balloon 114 that may be inflated by injecting air or someother fluid into a tube 118 that is coupled to a proximal end of theballoon 114. It should be understood, however, that the expandableelement 110 is not limited to inflatable balloons and that other devicesor materials may be used to expand the implant 26.

As best shown in FIGS. 2B and 2C, the second body member 34 includes afirst plate 140, and a second cage body 144 that is coupled to thesecond plate 140. In particular, the second plate 140 is coupled to aproximal end of the second cage body 144. While the second plate 140 andthe second cage body 144 are shown as separate components that arecoupled together, it should be understood that the second plate 140 andthe second cage body 144 may be integrally formed as one piece.

As best shown in FIG. 2B, the second plate 140 includes a front facemember 142 that defines a fixation element receiving aperture 148 thatextends therethrough from a front side to a back side at a downwardangle. The fixation element receiving aperture 148 may define internalthreads that are configured to engage external threads defined by afixation element, such as bone screw 152, as the bone screw 152 isinserted into the fixation element receiving aperture 148. The bonescrew 152 is configured to engage the inferior vertebral body 10 b onceit is fully inserted to thereby brace or otherwise affix the second body34 against the vertebral body. The fixation element receiving aperture148 may be fully enclosed as shown in the illustrated embodiment, or thefixation element receiving aperture 148 may be partially enclosed tothereby define for example a semi-circle. The fixation element receivingaperture 148 may be configured to receive a fixation element other thanthe bone screw 152. For example the fixation element receiving aperture148 may be configured to receive blades or nails. Therefore, thefixation element receiving aperture 148 may be void of threads.Moreover, it should be understood that the second body member 34 may beconfigured to be braced against the vertebral wall of the vertebral bodyusing structure other than fixation elements. For example, the secondbody member 34 may be toothed so as to not allow the second body member34 to rotate when the implant is inserted.

As shown, the front face member 142 also defines a holding aperture 154that extends therethrough adjacent to the fixation element receivingaperture 148. The holding aperture 154 is configured to receive aninsertion tool so as to couple the implant 26 to the insertion tool forinsertion of the implant 26 into the intervertebral space 18. Theholding aperture 154 may include internal threads that are configured toengage external threads defined by the insertion tool to therebysecurely couple the implant 26 to the insertion tool during insertion.As shown, the holding aperture 154 may also be substantially alignedwith the channel 102. Therefore, the expandable element 110 may beinserted into the channel 102 through the holding aperture 154 as shownin FIGS. 2D and 2E.

As shown in FIG. 2B, the second plate 140 also defines a curved externalsurface 156 that is generally convex. As shown, the curved externalsurface 156 is positioned such that it is adjacent the curved surface 56of the first body member 30. The curved surfaces 56 and 156 correspondto each other such that as the first body member 30 rotates relative tothe second body member 34 the first and second plates 40 and 140 canslide past each without substantial interference.

As shown in FIGS. 2A and 2B, the second cage body 144 is elongate in thelongitudinal direction L. The second cage body 144 defines an upper orsuperior or outer transverse bone engagement or contacting surface 160configured to contact the superior vertebral body 10 a, and a lower orinferior or outer transverse bone engagement or contacting surface 164configured to contact the inferior vertebral body 10 b. Both outercontacting surfaces 160 and 164 may include teeth 68 that are configuredto engage the superior and inferior vertebral bodies 10 a and 10 b. Asshown, the teeth 68 may be aligned in arcs with the centre of these arcsbeing proximate to the hinge 38.

As shown in FIG. 2B, the second cage body 144 includes an elongate bodyportion 170 that extends in the longitudinal direction L, and a secondjoint 174 that extends proximally from the elongate body portion 170 andat least partially toward the first body member 30. In the embodimentshown, the joint 174 extends substantially perpendicularly from theelongate body portion 170 toward the first body member 30. As shown, thecage body 144 also includes a free end 178 that extends distally fromthe elongate body portion 170 and at least partially toward the firstbody member 30. Therefore, because both the first joint 174 and the freeend 178 at least partially extend toward the first body member 30, thesecond cage body 144 generally defines a C-shaped structure.

As shown, the second joint 174 includes a plate 182 that is configuredto engage the gap 86 defined between the two plates 78 of the firstjoint 74. The plate 182 defines an aperture 190 that extends completelytherethrough in the transverse direction T. As shown, the aperture 190is configured to align with the apertures 90 of the first joint 74 whenthe plate 178 is received in the gap 86. The apertures 90 and 190 shouldalign so that the pin 94 can engage each aperture 90 and 190 to therebydefine the hinge 38. As shown in FIG. 2C, the hinge 38 defines a pivotaxis that extends in the transverse or caudal-cranial direction.Therefore, at least one of the first body member 30 and the second bodymember 34 may rotate about the rotation axis in the horizontal planedefined by the longitudinal and lateral directions to thereby increasethe overall footprint of the implant 26. It should be understood thatthe joints 74 and 174 may part of either the first body member 30 or thesecond body member 34. Moreover, the hinge 38 may be defined bystructure other than the joints 74 and 174. For example, the first bodymember 30 and the second body member 34 may integral parts that areconnected by an integral hinge 38 that allows at least one of first bodymember 30 and the second body member 34 to rotate relative to the other.

The free end 174 of the second cage body 144 defines a second matingfeature 194. As shown, the second mating feature 194 includes aprotrusion 198 that extends toward the recess 98 of the first bodymember 30. The second mating feature 194 is configured to mate with thefirst mating feature 94 when the implant 26 is in an unexpandedconfiguration. In particular, the protrusion 198 is configured to engageor otherwise extend into the recess 94 of the first body member 30 whenthe implant 26 is in an unexpanded configuration. As shown in FIG. 2D,when the implant 26 is in its unexpanded configuration, the first cagebody 44 and the second cage body 144 (or at least their elongate bodyportions 70 and 170) are spaced apart such that a cavity 200 is definedbetween the elongate body portions 70 and 170. As shown, the cavity 200is generally oval shaped and the overall implant 26 generally defines anoval shaped ring when the implant 26 is in an unexpanded configuration.Though, it should be understood that the cavity 200 or at least theimplant 26 may include other shapes as desired when the implant 26 is inits unexpanded configuration.

As shown in FIGS. 2D and 2E, the expandable element 110 may be insertedthrough the holding aperture 154 and into the channel 102 until a atleast a portion of the expandable element 110 is within the recess 98 ofthe first body member 30 and adjacent to the protrusion 198. When theexpandable element 110 is activated, the expandable element 110 willcontact and apply a force to the protrusion 198 thereby causing at leastone of the first body member 30 and the second body member 34 to rotateabout the hinge 38. As the body members 30 and 34 rotate, the protrusion198 recedes from the recess 98 such that the free ends 74 and 174 of thebody members 30 and 34 move away from each other. The free ends 74 and174 can be said to move away from each other if the protrusion 198 iscompletely disengages from the recess 98 or if the protrusion 198partially disengages from the recess 98 so long as the protrusion 198 atleast partially recedes from the recess 98.

In operation and in reference to FIGS. 3A-3I, the implant 26 may beinserted into the intervertebral space 18 while in an unexpanded. Asbest shown in FIG. 3D, the implant 26 may have an initial insertion orotherwise first width W1 when the implant 26 is being inserted into theintervertebral space 18. The initial width W1 may be narrow enough toallow for a minimally invasive approach to thereby reduce damage to thepatient. Once the implant 26 has been inserted into the intervertebralspace 18, the first bone screw 52 may be inserted into the fixationelement receiving aperture 48 of the first body member 30 and into thesuperior vertebral body 10 a, as shown in FIGS. 3B-3D. At this point thefirst body member 30 may be securely fixed to the superior vertebralbody 10 a.

As shown in FIGS. 3E and 3F, the expandable element 110 then be insertedthrough the holding aperture 154 and into the channel 102 so that atleast a portion of the expandable element is proximate to the matingfeatures 94 and 194. The expandable element 110 may then be activated orotherwise expanded so as to apply a force to the mating feature 194 tothereby cause the second body member 34 to rotate relative to the firstbody member 30 about the hinge 38 and expand the implant 26 to itsexpanded configuration. As best shown in FIG. 3F, the implant 26 mayhave an expanded or otherwise second width W2 that is greater than thefirst width W1 when the implant 26 is in the expanded configuration. Asshown, when in the expanded configuration, the implant 26 has a greaterfootprint to thereby increase stability of the implant.

Once the implant 26 has been expanded, the second bone screw 152 may beinserted through the fixation element receiving aperture 148 of thesecond body member 34 and into the inferior vertebral body 10 b, asshown in FIGS. 3G and 3H. Once the bone screw 152 has been affixed tothe inferior vertebral body 10 b, the implant 26 will be securelyaffixed to the vertebrae such that the first and second body memberswon't rotate or otherwise change their orientation, as shown in FIG. 3I.

It should be understood that the second body member 34 may be affixed tothe inferior vertebral body 10 b first, rather than affixing the firstbody member 30 prior to expanding the implant 26 to its expandedconfiguration. Furthermore, it should be understood that the implant 26may be expanded to its expanded configuration prior to any of the firstand second body members 30 and 34 being affixed to the superior andinferior vertebral bodies 10 a and 10 b. Therefore, the implant 26 maybe expanded unilaterally by affixing one of the body members 30 and 34prior to expansion, or bilaterally by expanding the implant 26 prior toaffixing any of the body members 30 and 34 to the vertebrae. In eithercase, due to the expansion of the cavity 200 between the first andsecond body members 30 and 34, the cage or at least the cavity 200 maybe filled with filler material (e.g. autologous, allograft bone, bonefiller substitute) after implantation of the implant 26. This could beachieved through injection or packing of the material into the cavity200.

In another embodiment and in reference to FIGS. 4A and 4B, the implant26 may be expanded by inserting an expandable element 110 directly intothe cavity 200. In this embodiment, there may be no need for the channel102. For example, as shown in FIGS. 4A and 4B, the expandable elementmay be inserted through the holding aperture 154 and into the cavity200. Once positioned, the expandable element 110 may be activated orotherwise expanded and force the body members 30 and 34 to rotaterelative to each other about the hinge 38. It should be understood,however, that the expandable element 110 may be inserted directly intothe cavity 200 without going through the holding aperture 154.

Although the disclosure has been described in detail, it should beunderstood that various changes, substitutions, and alterations can bemade herein without departing from the spirit and scope of the inventionas defined by the appended claims. Moreover, the scope of the presentdisclosure is not intended to be limited to the particular embodimentsdescribed in the specification. As one of ordinary skill in the art willreadily appreciate from the disclosure of the present invention,processes, machines, manufacture, composition of matter, means, methods,or steps, presently existing or later to be developed that performsubstantially the same function or achieve substantially the same resultas the corresponding embodiments described herein may be utilizedaccording to the present disclosure.

What is claimed:
 1. An intervertebral implant configured to be implantedinto an intervertebral space between first and second vertebral bodiesthat are spaced from one another along a first direction, the implantcomprising: a first body member having a first surface and a secondsurface opposite one another along the first direction, and a firstconvex lateral sidewall and a first concave lateral sidewall that extendbetween first and second surfaces, the first body member defining achannel that extends at least partially through the first body betweeninternal surfaces of the first convex lateral sidewall and the firstconcave lateral sidewall; a second body member adjacent to the firstbody member, the second body member having a first surface and a secondsurface opposite one another along the first direction, and having asecond convex lateral sidewall and a second concave lateral sidewallbetween the first and second surfaces of the second body member; and anexpandable element within the channel adapted to expand so as to move atleast one of the first and second body members to move the implant froman initial configuration to an expanded configuration, wherein at leastone of the first and second body members is movable in a direction awayfrom the other one of the first and second body members as the implantmoves from the initial configuration to the expanded configuration,wherein the first body member defines a recess and the second bodymember defines a mating feature, at least a portion of the matingfeature within the recess in the initial configuration and the portionof the mating feature disposed outside the recess in the expandedconfiguration; and wherein the first convex lateral sidewall and firstconcave lateral sidewall are offset from one another alone a seconddirection, perpendicular to the first direction.
 2. The implant of claim1, wherein expansion of the expandable element within the channel biasesthe at least one of the first and second body members away from theother one of the first and second body members.
 3. The intervertebralimplant of claim 1, wherein the recess is defined between opposingsurfaces of the first body member that are offset from one another alongthe first direction.
 4. The intervertebral implant of claim 1, whereinsecond body member includes a protrusion that extends towards thechannel of the first body member.
 5. The intervertebral implant of claim4, wherein the protrusion is configured to extend into the channel ofthe first body member.
 6. The intervertebral implant of claim 1, whereinthe portion of the second body member rides within the first body memberas the implant is expanded from the initial configuration to theexpanded configuration.
 7. The intervertebral implant of claim 1,wherein the implant is configured to remain in the expandedconfiguration after the expandable element has been removed.
 8. Theintervertebral implant of claim 1, wherein the first and second bodymembers together define an opening therebetween when the implant is inthe expanded position.
 9. The intervertebral implant of claim 8, whereinthe opening expands as the at least one of the first and second bodymembers expand in the direction away from the other one of the first andsecond body members.
 10. The intervertebral implant of claim 1, whereinthe expandable element is elongate as it extends between an insertionend and a trailing end of the implant.
 11. The implant of claim 1,wherein the expandable element is removable from the channel when theimplant is in the expanded configuration.
 12. The implant of claim 1,wherein the expandable element is an inflatable balloon.
 13. The implantof claim 1, wherein an exterior surface of the mating feature is curvedand an exterior surface of the first body that defines the recess iscurved.